Druckverlauf und Gasdruckschwingung im Schaufelkanal von Seitenkanalverdichtern

The pressure in the impeller, in the side channel and in the breaker of a side channel compressor with the polytropic compression and with the polytropic expansion of the breaker mass flow was investigated experimentally, and the occurring shock waves were detected during the expansion of the gas in the breaker. Thereby different pressure flows occur at the four measuring points in blade channel on the blade pressure and suction side of the related radius from r _i /r ₂=0.80 and r _i /r ₂=0.95, which give an indication of the blade channel flow. In addition to the periodic increase in pressure and the gas expansion in the breaker, the superimposed pressure oscillation in the side channel is caused by the blade rotation frequency. This superimposed pressure oscillation can be decomposed by Fourier transformation in the two pressure oscillation components. These phenomena are the reason for the more accurate investigation of the pressure flow in the blade channel during the polytropic compression and expansion of the breaker mass flow. The gradient of the effective values of the gas pressure oscillation in the blade channel leads not only to the operating characteristics of the side channel compressor ??p=f(?,n), but also to the breaker curve characteristic ??p _U =f(?,n).     

Spezifische Energieverteilung im Kanal von Seitenkanalverdichtern

Distribution of energy in the channel of side channel compressors With dynamic pressure sensors, the total pressure and dynamic pressure share can be measured in any density of the side channel profile. The dynamic progression of gas pressure, which appears as gas pressure oscillation, can be characterized by peak value of gas pressure oscillation, RMS and amplitude value p_A of gas pressure oscillation at blade rotary frequency. Out of it, the regions of intense transport of specific momentum and intense energy transfer in side channel can be ascertained. Out of the distribution of velocity in side channel profil in association with the distribution of pressure, the distribution of specific energy in side channel can be ascertained as well.     

Gasdruckschwingungsverteilung im Arbeitskanal von Seitenkanalverdichtern

The magnitude of energy transfer in side channel compressors depends on intenseness of gas pressure oscillation and transport of specific momentum in the side channel. For analysis of energy transfer from impeller to gas, the static pressure distribution and the intenseness of gas pressure oscillation in meridian profile of the side channel subject to radius and also to axial distance to impellers grid was measured with a high tightness of reading points. In order to plot the intenseness of gas pressure oscillation in meridian profile of the side channel, gas pressure oscillation in side channel has been characterized by RMS, peak value and amplitude value of gas pressure oscillation at blade rotation frequency. The results of gas pressure oscillation and tangential velocity progression in side channel from laser measurement show that the strongest gas pressure oscillations and highest velocities appear in outer region of the impeller and side channel, which refer to intense energy transfer in this region.     

Dämpfung von Rotating Stall in Radialverdichterstufen

In part load span centrifugal compressors incline rotating stall in the impeller, which often causes transient pressure oscillations and surge. Operation in part load span with transient processes has to be avoided, because it can endanger the compressor and the plant by vibrations. Active devices like an upstream or downstream side channel stage can influence flow and unsteady gas pressure oscillations in centrifugal compressor stages and shift rotating stall to lower flow or entirely avoid it. This article shows experimental results for characteristic lines and unsteady gas pressure oscillations in centrifugal compressor stages, which where coupled with an downstream side channel stage. The enforced turbulent eddy flow with unsteady gas pressure oscillation in side channel stages diminishes unsteady gas pressure oscillation in the centrifugal compressor stage and limits pressure gradient as well as the maximum reachable value of gas pressure oscillation at rotating stall.     

Druckschwingungsverteilung im Seitenkanal von Verdichtern

Distribution of the pressure oszillations in the side channel of compressors The investigation of the unsteady pressure field in side channel machines with high pressure coefficients of ψ_n = 3,5 to 34 gives a better understanding of the unsteady turbulent vorticity flow in the impeller and the side channel and also of the energy transfer. The impeller with high number of blades generates a turbulent vorticity flow, which exists over the entire side channel. The specific momentum causes pressure oscillations of p(t) = 250 Pa to 9,0 kPa also in the entire side channel which lead to an increase of the static pressure in the circumference of the side channel. The oscillation of the pressure is exited by the blade passage frequency and the frequency of the turbulent vorticity flow, with the lower frequencies having priority to the energy transfer. It also leads to dissipation losses limiting the efficiency and causing a heat up of the gas.     

Druckschwingungen in Seitenkanalpumpen

By the turbulent vortex forced by the impeller, strong high-frequency pressure oscillations occur in the side channel. These pressure oscillations result from the temporal modification of the vortex structure and the specific impulse flow transportation in the side channel. They are visible due to the high-frequency character neither at integral static pressures not in the characteristic lines of the pumps. However, they add essentially to the energy transfer to the pumped fluid and to the increase of the static pressure in the side channel. The dynamic pressure oscillations in the side channel with the characteristic exciter frequency by the blade revolution frequency are transmitted to the pump case and a part of it is emitted as effective acoustic pressure to the environment. The blade revolution frequency is by far recognizable as exciter frequency in the pressure oscillations, in the mechanical case oscillation and as effective acoustic pressure in the raised amplitude parts. The pressure oscillations refer to the unsteady flow in side channel pumps.     

Auslegung und Gestaltung von hochtourigen Kleinstverdichtern

Dimensioning and designing of highspeed small compressors In the medical engineering and within the range of the physical technology often low air and gas volume flow rates at low pressures of Δp = 10 kPa to 20 kPa are needed for the air supply and for heaters or coolers. Side channel compressors are suitable for it in a special way because side channel compressors are suitable for little volume flow rates and high pressure coefficients, i.e. for small diameter numbers and low speed numbers. Also strict requirements on dimensions, weight and the noise emitted are made to small compressors. These demands lead to high numbers of revolutions and to high blade rotation frequencies with the usual peripheral velocity of the impeller of u_a = 70 m/s to 80 m/s. With these moderate peripheral velocity there are no considerably high sound pressure levels, but higher blade rotation frequencies in comparison with large side channel compressors. The high frequency noises can be dammed by secondary active noise control measures more easily than low‐frequency noises which is a great advantage.     

Kombination von Radial- und Seitenkanalstufen für Turboverdichter

Unsteady gas pressure oscillations occur at impeller outlet and diffuser of radial and side channel compressors, engendered by the blades grid of the impeller. They have effect beyond the limits of inlet and outlet. If a radial stage is coupled to a side channel stage, then the unsteady gas pressure oscillations of the side channel stage have an effect inside the radial stage affecting flow and characteristic curve. Because of that, the radial stages unstable characteristics and the limit of rotating stall can be moved to lower volume flows or completely suppressed by connecting a side channel stage before or behind it. Therefore the permissible range of operation of combined compressor stages can be extended compared with a radial compressor stage. Moving the limit of rotating stall of the radial compressor stage and lower the gas pressure oscillations caused by Rotating Stall as a result of the side channel stages unsteady gas pressure oscillations will be proved experimental. As a criterion for Rotating Stall in radial compressor stages also the proportion between RMS of gas pressure oscillations and the total pressure increase in the radial compressor stage can be used.     

基于转静干涉效应的压气机叶片气动载荷分析

转静叶排的相互作用会使压气机内部流场存在复杂的非定常性。为深入研究压气机叶片的气动载荷特性,以某型航空发动机压气机为研究对象,考虑叶排间的转静干涉效应,利用滑移网格技术对整个叶盘的三维流场展开模拟,求解干涉周期T_b内压气机转子内部的流动规律。同时对叶片气动载荷的非定常特性进行进一步分析,讨论了不同压比、转速对压气机叶片气动载荷的影响。结果表明叶片压力面和吸力面气动载荷波动峰值的主导频率皆为转静干涉频率f₀的倍频,其中一倍频（1×f₀）分量占主导地位。在干涉周期T_b内,叶片表面压力涡发生周期性的迁移与耗散,压力面和吸力面气动载荷的变化呈相反趋势。随着压比的增加,压气机叶片气动载荷逐渐增大,但其脉动幅值和频谱峰值基本不变。转速的升高使得转静干涉的频率增大,增强了压气机叶片气动载荷的非定常特性。研究结果能够应用于叶盘结构的气动优化设计,可为高性能航空发动机压气机的研制提供支持和参考。     

Strömungstechnisches und thermodynamisches Verhalten von Seitenkanalverdichtern im Vakuumbereich

Because of the lower gas density side channel compressors perform in vacuum operation better fluidic performace than in pressure operation for generating overpressure. The thermal load of the compressors is reduced by the lower final compression temperature. The polytropic expansion of the lower mass flow in the breaker, which removes thermal energy both from the expanding gas and from the housing and therefore causing a cooling of the compressor, contributes especially to the varied thermodynamic performance in vacuum operation. This inner thermodynamic performance of the compressor in the breaker area and the suction area provides together with the lower power absorption an advantageous performance of side channel compressors in vacuum operation at absolute pressures p _S=10 to 40 kPa. These advantages in operation and thermodynamic advantages are as bigger as higher the vacuum and as lower the gas density get. From this a promising development of side channel compressors as vacuum pumps also in a higher vacuum region can be deduced.     

Isotropie der turbulenten Wirbelströmung in Seitenkanalverdichtern

The impeller with a high number of blades causes a turbulent vorticity flow in the side channel, which is the reason for the specific impuls flow and the energy transfer in the side channel. High frequency pressure oscillations were caused according to the changes of the vorticity structure in the side channel. The dissipation loses are the reason for the heat up of the gas during the compression. According to the transported gas mass flow the turbulent vorticity flow is superposed from the average flow velocity of the gas. They depend from the peripheral speed of the impeller and the size of the compressor. The superposition of the turbulent vorticity flow and the average flow velocity cause the question of the isotrope of the turbulent vorticity flow in the side channel for the working area of the compressor. Experimental results from side channel compressors will give an answer to this.     

Grenzbereiche von Seitenkanalverdichtern im Vakuumbetrieb

The kinematic viscosity of the gas rapidely rises with decreasing suction pressure in the vacuum region, which leads to a decrease of the reynolds number of the flow in the side channel and to a laminar flow structure which may cause a modification of the side-channel-compressor behavior during the energy transfer. By the reduced density of the gas in the vacuum region of the side channel compressor the mass flow and the transfered specific enthalpy are decreased with constant volume flow. Through that, the specific growth of enthalpy during the compression and during the expansion of the mass flow in the breaker decreases. This leads to a decrease in the growth of the temperature during the compression at the same pressure ratio and the thermal load of the compressor is reduced. The polytropic change of state of the gas during the compression approaches an adiabatic change of state for decreasing suction pressure in the vacuum region. The polytropic change of state of the expansion flow in the breaker approaches the theoretical expected isothermal change of state for decreasing suction pressure, whereby side channel compressors are relieved of thermal load and higher pressure ratios are within reach. So the breaker of the side channel compressor, which causes in pressure operation mode high specific dissipation losses and leads to high polytropic exponents effects in the higher vacuum region thermodynamic advantages of the pressure region.     

Schalldruckverteilung in Seitenkanalverdichtern

ZusammenfassungIn Seitenkanalverdichtern arbeitet das Laufrad mit hoher Schaufelzahl am Rand des torusförmig am Umfang angeordneten Seitenkanals mit instationärer Strömung. Dabei durchläuft das Schaufelgitter das gesamte instationäre Druckfeld von p _S bis p _D sowie den Unterbrecher mit der Gasexpansion, der den Saugstutzen vom Druckstutzen trennt. Dadurch entstehen im Seitenkanal und besonders an den Unterbrecherein– und Austrittskanten Gasdruckschwingungen, die das Verdichtergehäuse zu mechanischen Schwingungen anregen und die auch als Schalldruck an die Umgebung abgestrahlt werden. Durch die große Schaufelzahl von z=36 bis 80 treten bei Antriebsfrequenzen von f=50 Hz und 60 Hz hochfrequente störende Geräusche von f _S=z f=1,8 bis 4,80 kHz auf, die als tonale Komponenten im Frequenzspektrum des Schalldruckpegels auftreten. Die störenden Geräusche, insbesondere die tonalen Anteile bei den erregenden Drehfrequenzen von f=50 Hz und 60 Hz können durch strömungstechnische und konstruktive Maßnahmen gemindert werden.In side channel compressors the impeller with high blade number works marginal of the circular at the perimeter disposed side channel with unsteady flow. Thereby the impellers grid with high blade number passes through the entire unsteady pressure field from p _S to p _D and the breaker with gas expansion, which separates inlet from outlet. Thus gas pressure oscillations accrue in side channel and especially at the breakers edges of entry and exit, which cause vibrations of the compressors casing and also are beamed as acoustic pressure to the environment. Because of the high blade number from z=36 to 80 at propulsion frequencies of f=50 Hz and 60 Hz high frequency disturbing noises of f _S=z f=1,8 to 4,80 kHz occur, which manifest as tonal components at these frequencies in frequency spectrum of acoustic pressure level. The disturbing noises, especially tonal components at rotary frequencies of f=50 Hz and 60 Hz, can be diminished by fluid mechanical and design features.     

Kopplung von Gasdruckschwingungen in Radialverdichtern

Unsteady flow processes occur in centrifugal compressors, especially noticeable in passing region between impeller flow and reposing diffusers like return bend or radial diffuser. This unsteady flow causes gas pressure oscillations of considerable extent. If the unsteady flow generates two or more gas pressure oscillations, which result of different arousals with different frequencies, interconnection of gas pressure oscillations occur, leading into new vibration occurrences and side bands at base frequency in frequency spectrum. If frequencies and magnitude of pressure oscillation amplitudes of single oscillations with sinusoidal oscillation progression are known, the resulting gas pressure oscillation progression of interconnected gas pressure oscillations can be calculated and also experimental proven.     

Wrap of cylinder and its effect on main features of rotary vane compressor for automobile air conditioning system

The rotary vane compressor has been used in the automobile air conditioning system. One of the key factors of its design is the wrap of its cylinder. From the working principle of this type of compressor, it is explained in mathematics why the wrap is composed of four parts: arc of circle, main curve, and two segments of transit curves, and the conditions that the wrap needs to satisfy are derived simultaneously. At the same conditions, we compared to the gas force F_p, contact force F_nc of the blade head, the force acting on rotor by blades, and the suction volume V_s for three kinds of main curves. The wrap composed of trigonometric function can form the biggest value of V_s, while the least suction volume V_s will be reached as the cubic polynomial is taken. The wrap composed of trigonometric function forms the biggest absolute value of the gas force F_p and the middle peak value of the force acting on rotor by blades, while the least absolute value of the gas force F_p and the biggest contact force F_nc of blade head will be reached as the cubic polynomial is taken. The force acting on the rotor by blades takes the biggest peak value if the main curve is the ellipse curve. The frequency of the force acting on the rotor by blades is the same as the number of blades at the range of the crank angle from 0 to 180°.     

Investigation on the effects of blade corrosion on compressor performance

Corrosion is a common reason for marine gas turbine blade failure, and salt spray is largely responsible for corrosion of metallic objects near the coastline. It will directly lead to geometrical deviations of the compressor blade, forcing an increase in roughness height of the surface of the blade. By using a three-dimensional numerical method, this paper deals with the corrosion of a 1.5 stage axial compressor. Two different schemes, respectively based on blade geometrical model modification and turbulent near wall functions, were employed in numerical simulations for corrosion rate of the blades. The compressor map, derived from the numerical simulations by adjusting the back pressure, shows that there is a decline of compressor efficiency and pressure ratio when the blade is corroded, which will result in performance degradation of the compressor. The corrosion properties of stainless steel were studied, using the static salt spray corrosion test under laboratory conditions. Additionally, combined with numerical methods, the compressor performance parameters along the extension of operating time were simulated and a binomial relationship between performance degradation and corrosion time was established. This research provides a technical guide for compressor performance prediction under less than ideal conditions.     

基于气流激振的离心式压缩机管道破坏机理研究

大型石化压缩机组中,管道易产生气流激振作用下的疲劳破坏。本文从气流激振的产生与作用机理进行分析,研究管道疲劳破坏的主要来源-声共振。采用实验室的管道声腔进行仿真分析,应用LMS仿真软件有限元法对管道内部的声模态进行计算,获取其特征频率,并进行实验测试分析,当叶片的通过频率与管道声模态频率一致时将产生声共振,振动将明显增加,揭示了声共振造成的管道疲劳破坏机理。在此基础上,结合实际大型离心式压缩机组管道振动控制的实例,证明了此方法的有效性,为大型离心式压缩机组管道的高周疲劳破坏抑制提供依据。     

Geschwindigkeit der Expansionsströmung am Unterbrecheraustritt von Seitenkanalverdichtern

The expansion flow of this breaker mass flow of side channel compressors decisively influences the intake flow of the gas mass flow in the side channel and so affects the energy transfer and the increase of pressure in the front area of the side channel. This causes a decrease of pressure and losses in this area. By taking measurements of the dynamic pressure fluctuations in the side channel it could be shown that in this area of the side channel the greatest pressure oscillations and with that the highest root main square of the dynamic pressure oscillation occure which finally lead to vortex formation with great losses of pressure. For this reason a decrease of pressure in the inlet area of the side channel is caused which leads to reduction of the increase of pressure. Suggestions for the improvement of the contour of the inlet of the side channel with less decrease of pressure and density are made.     

Experimental investigation of a CO2 automotive air conditioner

In this study, a CO₂ automotive air conditioner prototype was designed and constructed. The compressor was of swash plate design; the gas cooler and evaporator were made of fin-tubes; a manual expansion valve and an internal heat exchanger accumulator were used. The lubricant, the CO₂ charge, the evaporator outlet pressure, the compressor speed, the air inlet temperature and flow rate of the gas cooler and the air flow rate of the evaporator were varied and the performance of the prototype was experimentally investigated in detail. The cooling capacity, compressor power consumption, CO₂ mass flow rate, and COP value were analyzed. The experimental results showed that the CO₂ system performance was greatly affected by different lubricants; the CO₂ system performance was sensitive to the mass charge; the high side pressure affected the system performance greatly and a high side pressure controller was needed.     

气液混输下侧流道泵内压力脉动特性研究

侧流道泵是一种新型超低比转速泵,因其具有小流量、高扬程、可自吸和气液混输等优点,近年来广泛应用于化工、汽车、医药工业和油气开采等领域。由于侧流道泵内部流动复杂、湍流强度极大,势必会产生较强的压力脉动,造成侧流道泵性能降低和运行不稳定,这种影响在气液混输时更为严重。基于MUSIG模型,对不同含气率下侧流道泵内部流动进行数值计算,并对气液混输工况下侧流道泵压力脉动特性进行研究分析。结果表明:MUSIG模型可适用于侧流道泵气液混输数值计算;少量通气有助于改善侧流道泵内绝大部分区域流态,但会导致轴向间隙处出现严重的压力脉动,这也是侧流道泵气液混输时运行不稳定的主要因素;低进口含气率(IGVF)下,压力脉动主频与含气量无关,始终等于轴频的整数倍;叶轮内压力脉动幅值始终大于侧流道的压力脉动幅值。该研究为气液混输工况下侧流道泵的优化设计提供基础依据,具有重要的工程应用价值。